ENH: Added GeometricField copy constructor with additional BC handling. See #1620

Often we want to copy a field and replace boundary conditions, e.g. change type
to calculated for some patches.  This has typically been achieved by creating a
word list of new patch types which are then fed through to the fvPatchField::New
factory method.  This is OK for types that require no additional input (usually
from dictionary) but leaves other more complex types partially
constructed/usable.

The new constructor clones all BCs except those with indices specified, for
which the fvPatchField::New method is called for the supplied patch field type.